This invention relates to camshafts for reciprocating piston engines. More particularly, this invention is a new camshaft and a new method of making a camshaft in which bearings, cams and the like are produced as individual parts and are fastened to the shaft.
The U.S. Pat. No. 4,382,390, issued May 10, 1983, to Friedrich Jordan and entitled, "Camshaft for Reciprocal Piston Engines", shows a camshaft in which bearings, cams, and the like are produced as individual parts and are fastened to the tube. In the Jordan camshaft, a tube is expanded by hydraulic or rubber means to conform the outside wall of the tube with the inside surface geometry of the cams and bearing rings. However, a big disadvantage in making the Jordan camshaft is that the wall and the axis of the tube inside the cams is completely offset from the wall and the axis of the rest of the tube. Thus, it is necessary that the cams be inserted into a die which corresponds to their outer shape in order to be sure that the widening of the hollow shaft will not cause substantial deformation of the cams.
The camshaft for a reciprocating piston engine and the method of making such a camshaft of this invention does not require that portions of the tube wall be completely offset to an axis different from the axis of the rest of the tube. Therefore, the forces necessary to interlock the cams and bearing rings with the tube are far less than the forces required by Jordan and usually the specially formed die required by Jordan is unnecessary.
Other current methods for making camshafts in which bearings, cams, and the like are produced as individual parts and fastened to a tube include uniformly expanding a tube to interlock with axial splines in the cam inside diameter. A uniform internal pressure is applied to expand the tube to uniformly match the outside diameter of the tube with the inside diameter of the cam. At this pressure, the cam is not yet stressed and no tube material has flown into the splines. In order for material to flow into the splines, the internal pressure in the tube must be increased. At the higher pressure, as the tube material flows into the splines, the cylindrical inside diameter portion of the cam is stressed. The resulting tensile stresses in the cam inside diameter tend to cause cracks if the cam is not in the soft state of heat treatment. Even if the cam is in the soft state, the stress situation is undesirable and is typically countered by the application of external pressure on the cam equivalent to that of the internal stresses. To apply the external stressing, some means of pressurization is set-up, such as a die or hydraulic system which always increases costs.
The camshaft for a reciprocating piston engine and the method of making such a camshaft of this invention require much smaller total energy (forces). The stressing of the inside diameters of the cams and bearings is essentially eliminated. Thus, fully hardened cams and bearings can be readily attached to the tube at very low cost.